Globulus Genotypes Research Articles

Climate and water availability impacts on early growth and growth efficiency of Eucalyptus genotypes: The importance of GxE interactions

Predicting Eucalyptus plantation productivity in the face of climate change is a key challenge for intensively managed forest plantations around the world. Forest industry tree improvement and advanced silvicultural programs are charged with maximizing forest production but face challenging selection choices where Eucalyptus genotypes may be sensitive to genetic × environment interactions (GxE). Our study investigated the importance of GXE interactions by measuring the early (establishment to 2.6 years old) cumulative growth response of 30 selected genotypes of Eucalyptus globulus, E. nitens, E. badjensis, E. smithii, E. nitens × globulus and E. camaldulensis × globulus hybrid seedlings established across contrasting water availability conditions (High vs Low Irrigation). We compared the same genotypes at a low vapor pressure deficit (VPD) and clayey soil (North site) and a high VPD sandy soil (South site) in order to evaluate the stability of these genotypes across environmental gradients and thus evaluate the importance of genetic versus environmental impacts on growth. Stand growth was evaluated at 2.6 years when leaf area index (LAI) reached canopy closure in order to estimate a growth efficiency relationship (GE) with current annual increment (CAI). As expected, irrigation increased cumulative growth and LAI for all taxas, except for E. smithii at the North site. Genotypes showed large significant differences of performance within and across sites under each irrigation treatment. However, a strong relationship between North and South cumulative volume at age 2.6 years was observed for irrigated genotypes but not for non-irrigated genotypes. This suggests that a large GxE interaction may be expected under low water resource availability conditions associated with strong effects in ranking change of evaluated taxas and genotypes. Comparing taxas with at least two genotypes or more in our experiment, GE increased under High Irrigation for all taxas across sites. However, E. nitens × globulus hybrids showed small differences between High vs Low Irrigation treatments GE relationships compared to E. nitens and E. globulus genotypes. Our results suggest the need for strategic allocation of genotypes to contrasting drought risk environments and the need to assess our understanding of how particular genotypes interact with water stress conditions.

Exploring the factors affecting carbon and nutrient concentrations in tree biomass components in natural forests, forest plantations and short rotation forestry

BackgroundCoupling biomass models with nutrient concentrations can provide sound estimations of carbon and nutrient contents, enabling the improvement of carbon and nutrient balance in forest ecosystems. Although nutrient concentrations are often assumed to be constant for some species and specific tree components, at least in mature stands, the concentrations usually vary with age, site index and even with tree density. The main objective of this study was to evaluate the sources of variation in nutrient concentrations in biomass compartments usually removed during harvesting operations, covering a range of species and management conditions: semi-natural forest, conventional forest plantations and short rotation forestry (SRF). Five species (Betula pubescens, Quercus robur, Eucalyptus globulus, Eucalyptus nitens and Populus spp.) and 14 genotypes were considered. A total of 430 trees were sampled in 61 plots to obtain 6 biomass components: leaves, twigs, thin branches, thick branches, bark and wood. Aboveground leafless biomass was pooled together for poplar. The concentrations of C, N, K, P, Ca, Mg, S, Fe, Mn, Cu, Zn and B were measured and the total biomass of each sampled tree and plot were determined. The data were analysed using boosted regression trees and conventional techniques.ResultsThe main sources of variation in nutrient concentrations were biomass component > > genotype (species) ≈ age > tree diameter. The concentrations of Ca, Mg and K were most strongly affected by genotype and age. The concentrations of P, K, Ca, Mg, S and Cu in the wood component decreased with age, whereas C concentrations increased, with a trend to reach 50% in the older trees. In the SRF, interamerican poplar and P. trichocarpa genotypes were comparatively more efficient in terms of Ca and K nutrient assimilation index (NAI) (+ 65–85%) than eucalypts, mainly because leafless biomass can be removed. In the conventional eucalypt plantations (rotation 15 years), debarking the wood at logging (savings of 225% of Ca and 254% of Mg for E. globulus) or the use of selected genotypes (savings of 45% of P and 35% of Ca) will provide wood at a relatively lower nutrient cost. Considering all the E. globulus genotypes together, the management for pulp with removal of debarked wood shows NAI values well above (× 1.7–× 3.9) the ones found for poplar or eucalypt SRF and also higher (× 1.6–× 4.0) than the ones found for oak and birch managed in medium or long rotations. The annual rates of nutrient removal were low in the native broadleaved species but the rates of available soil nutrients removed were high as compared to poplar or eucalypts. Management of native broadleaved species should consider nutrient stability through selection of the biomass compartments removed.ConclusionsThe nutrient assimilation index is higher in poplar grown under short rotation forestry management than in the other systems considered. Nutrient management of fast growing eucalyptus plantations could be improved by selecting efficient genotypes and limiting removal of wood. The values of the nutrient assimilation index are lower in the natural stands of native broadleaved species than in the other systems considered.

Transcriptome Profile in Response to Frost Tolerance in Eucalyptus globulus

The genetic improvement of trees for freezing tolerance is one of the most important goals to extend the plantations to colder areas. RNA-Seq technology has become a key tool in transcriptome studies. It can quantify overall expression levels for each gene simultaneously with high efficiency and speed through in silico gene expression, where differentially expressed genes can be identified by measuring the reads mapped for each transcript. In this study, the results of ESTs libraries from two Eucalyptus globulus genotypes showing contrasting differences in frost tolerance after cold acclimation using mRNA-Seq and in silico gene expression are discussed. A total of 14,265 non-redundant transcripts were predicted, where 163 corresponded to upregulated and 537 to downregulated genes. Pathway analyses of upregulated transcripts indicated that differences in frost tolerance might be regulated by the tree response to chemical and osmotic stimulus and organic substances, principally by overexpressing proteins that respond to hormone stress. These results suggest that genes coding for dehydrins, outer envelope, and voltage-dependent anion channel proteins are likely to participate in the regulation of the cold acclimation process and may have an important role in frost tolerance. The transcription factor analysis allowed identifying that those most differentially expressed in a resistant genotype were participating in the regulation of transcription, hormone regulation, photosynthesis, and response to stress. Additionally, the screening of polymorphic EST-SSR in silico and the validation of these markers in a reference population lead to identify a polymorphic EST-SSR with potential use for plant breeding and genotype discrimination.

Structural features of dioxane lignin from Eucalyptus globulus and their relationship with the pulp yield of contrasting genotypes

The chemical structure of dioxane lignins isolated from two groups of Eucalyptus globulus genotypes with contrasting pulpwood characteristics were evaluated. Six genotypes were selected and separated in two groups (G1 and G2) based on differences in wood density, pulp yield and chemical characteristics. Lignin was isolated from both milled wood and kraft pulps produced at kappa number 16, and were characterized by different techniques such as FTIR, elemental analysis, molar mass distribution and 31P NMR spectroscopy. From the different characteristics evaluated, some were determined as more relevant, such as syringyl (S) and guaiacyl (G) amounts, S/G ratio and condensed biphenyl units, were correlated with the pulp yield. High correlations were found between pulp yield and syringyl units (R2 = 0,69), and pulp yield and syringyl/guaicyl ratio (R2 = 0,88). The condensed 5-5 biphenyl units presented a negative correlation with pulp yield (R2 = 0,76). The information obtained explained part of the difference in pulpability of the contrasting genotypes and can be used for the selection and improvement of the species for the pulp and paper industry.

Retention and Structure of Xylans from Eucalyptus Globulus Genotypes with Different Pulpwood Characteristics

In this work, six different genotypes of Eucalyptus globulus were selected on the basis of their differences in wood density and pulp yield. The trees were separated into two groups of three genotypes each: group I (samples Eg1, Eg2, and Eg3) presented wood density values of 547–573 kg/m3 and pulp yields of 52.7–54.6%; group II (samples Eg4, Eg5, and Eg6) presented wood density of 471–485 kg/m3 and pulp yields of 49.8–52.3%. Chemical characterization showed that genotypes of group I also presented high glucose and low lignin content as compared with genotypes from group II. Xylans content was lower in samples of group I than group II. Kraft pulps from group I presented high retention of xylans in comparison with pulps from group II. This behavior was associated with a high degree of substitution (DS) of the xylose units with methylglucuronic acids in wood and in kraft pulps in samples of group I compared with group II. Xylans isolated from wood samples of group I also presented slightly higher molar mass than xylans from group II. Results showed that xylans from a single species presented differences in their retention and structure that affected the pulp yield of E. globulus.

Hormonal dynamics during recovery from drought in two Eucalyptus globulus genotypes: From root to leaf

Drought is a limiting environmental stress that represents a growing constraint to the forestry sector. Eucalyptus globulus is a widely planted coppice species, which capacity to cope with water deficit has already been described. However, the capacity of this species to recover is still poorly understood. In this study, we aimed to investigate the changes in abscisic acid (ABA), ABA-glucose ester (ABA-GE) and jasmonic acid (JA) content in leaves, xylem sap and roots of two genotypes (AL-10 and AL-18) during rewatering (2 h, 4 h, 24 h, and 168 h), after a drought stress period (0 h). We wished to clarify the role of these hormones in the recovery from drought and to determine whether these hormonal relations were related to specific genotype metabolisms. Our results showed that drought caused an increased in ABA and ABA-GE levels in all analysed plant parts, while JA content decreased in leaves, increased in xylem sap and did not change in roots. Some of these responses were genotype specific. During rewatering, ABA and ABA-GE content decreased in both genotypes and all plant parts, but at different time scales, and JA levels did not greatly change. Again, the genotypes responded differently. Altogether, our results characterised the response pattern of clone AL-10 as more responsive and defended that leaf should be used in preliminary screening methods of stress tolerance. The hormonal dynamics were related to the previously documented responses of these genotypes and sustain further physiological and molecular studies of water stress in this and other tree species.

Lignin chemistry and topochemistry during kraft delignification of Eucalyptus globulus genotypes with contrasting pulpwood characteristics

Abstract Eucalyptus globulus Labill. is a short-fibre resource for pulp and paper production. Ten different E. globulus genotypes with varied pulpwood quality and chemical composition were evaluated under kraft pulping conditions. Characterisation of the wood and pulp samples by thioacidolysis indicated that the content of syringyl units in β-O-4 linkages (S-β-O-4) was distinct for the studied genotypes. The highest S-β-O-4 levels were detected in the samples with the lowest original lignin and highest glucan levels. This group of samples provided the pulps with the lowest final lignin content at higher yields. UV microspectrophotometric (UMSP) evaluation of the wood chips revealed that the samples with the lowest lignin levels have the lowest UV absorbances at 278 nm (A278 nm) in the secondary walls (S2). During kraft pulping, lignin from the S2 was dissolved, whereas lignins from the middle lamella and cell corner lignin was not removed not even for prolonged reaction periods, independently of the evaluated genotype. The A278 nm values of the S2 were significantly lower in the pulps from the genotypes with less original lignin content.

Discovery, validation, and in silico functional characterization of EST-SSR markers in Eucalyptus globulus

Eucalyptus globulus is the most commonly planted hardwood species for pulpwood in temperate regions. We aimed to develop and characterize functional molecular markers for population genetic analyses and molecular breeding in this model tree species. Public expressed sequence tag (EST) databases were screened for nonredundant sequences to predict putative gene functions and to discover simple sequence repeats (EST-SSRs), which were then validated in E. globulus and six other Eucalyptus species. A total of 4,924 nonredundant sequences were identified from 12,690 updated E. globulus ESTs. Approximately 19.3% (952) were unigenes and contained 1,140 EST-SSR markers, which were mainly trimeric (58.6%). A set of 979 primers for putative SSR markers was designed after bioinformatic analysis. The predicted functions of these ESTs containing SSR were classified according to their gene ontology (GO) categories (biological process, molecular function, and cellular component). GO categories were assigned to 226 ESTs (30.2%). Most ESTs containing SSR (78.7%) had significant matches (E ≤ 10−5) with the nonredundant protein database using BLASTX. From a set of 56 random primer pairs, 37 could be validated in eight E. globulus genotypes and were also tested for cross-transferability to other six Eucalyptus species (Eucalyptus grandis, Eucalyptus saligna, Eucalyptus dunnii, Eucalyptus viminalis, Eucalyptus camaldulensis, Eucalyptus tereticornis). Seventeen polymorphic EST-SSR markers for E. globulus were evaluated in 60 unrelated trees, being representative of the species’ natural distribution. As a result, six highly informative markers were proposed for genetic diversity analyses, fingerprinting, and comparative population studies, between different species of E. globulus.

Functional markers development and genetic diversity analysis in Eucalyptus globuluswith emphasis in wood quality candidate genes

Eucalyptus globulus is the most planted hardwood species for pulpwood in temperate regions. Genomic researches in Eucalyptus have increased the information available in DNA sequences public databases and several structural and regulatory genes involved in the cellulose and lignin pathways are known. Functional genetic markers, while frequent in crop, are still scarce in forest species. Hence the detection and validation of SSRs in interesting genes to be used in future projects of marker-assisted breeding are needed. The present study aimed the development of novel functional markers (SSRs) in ESTs and wood quality candidate genes (CG) from Eucalyptus globulus ,a nd analyzes their potential for genetic diversity and individual identification studies. We report the design of SSR primers flanking simple sequence repeats in ESTs and CG, the validation of a subset of randomly selected EST-SSRs using eight E. globulus genotypes and the screening of a sample of 60 trees with the polymorphic SSRs. Also, SSRs cross-transferability was tested in seven Eucalyptus species coming from three sections: E. grandis, E. saligna (section Latoangulatae); E. globulus, E. dunnii, E. viminalis (section Maidenaria); and E. camaldulensis, E. tereticornis (section Exsertaria). Material and methods Plant material A total of 60 trees, each from a different OP family of E. globulus, were analyzed for their variability. These sixty trees represented major geographical races of the species’ natural distribution that were grown in a field trial in the Province of Buenos Aires, Argentina, between 1995 and 1997. For validation analyses one individual of each race (except Furneaux) was included. A total of 47 individuals from seven species (including E. globulus) of the genus were sampled for the transferability analyses. Methods

Transcript abundance of enzymes involved in lignin biosynthesis of Eucalyptus globulus genotypes with contrasting levels of pulp yield and wood density

One hundred genotypes of Eucalyptus globulus were ranked according to specific consumption of wood (cubic meters of wood needed to produce 1 ton of pulp). Ten of the most contrasting genotypes were separated in two groups of five clones each; group 1 (G1) with high wood density, high pulp yield, and low specific consumption, and group 2 (G2) with low density, low pulp yield, and high specific consumption. The contrasting genotypes also had significant differences in lignin content, percent syringyl unit composition, and frequency of β-O-4 linkages. Gene expression for phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), 4-coumarate:CoA ligase (4CL) and ferulate 5-hydrolase (F5H) was analyzed in the contrasting genotypes. In both groups, transcript abundance for CAD, PAL, and 4CL were similar and only F5H presented significant differences between groups, with high values in the best ranked genotypes G1 in comparison to G2. Correlations between traits were estimated for lignin content vs. pulp yield (R2 = 0.97), pulp yield vs. syringyl units (R2 = 0.82), β-O-4 linkages vs. pulp yield (R2 = 0.84), and β-O-4 linkages vs. syringyl units (R2 = 0.97). Correlations between chemical composition and transcript abundance for F5H were calculated, finding correlation values with lignin content (R2 = 0.81), syringyl units (R2 = 0.83), and pulp yield (R2 = 0.81). The measurement of transcript abundance of F5H represents a potential genomic tool for tree improvement programs to select trees with high pulp yield.

CLASSIFICATION OF GENOTYPES OF EUCALYPTUS GLOBULUS UNDER COLD CONDITIONS USING THEIR FREE AMINO ACIDS CONTENT ON LEAVES AND REGULARIZED DISCRIMINANT ANALYSIS (RDA)

ABSTRACT Eucalyptus globulus is an important forestry species for wood and pulp industry; however, its low cold resistance is a serious disadvantage. In this work, chemometric techniques were applied on the leaves’ free amino acid content of different E. globulus genotypes in order to select cold tolerant genotypes. Pattern recognition methods based on regularized discriminant analysis ( RDA ) were used to classify the genotypes by cold resistance using samples’ foliar damages as reference of cold resistance. Correlation between the amino acids content and cold resistance of genotypes was determined from a partial least squares ( PLS ) model. RDA models showed an excellent classification of genotypes (100% of correctly assigned genotypes in external validation), especially when RDA was reduced to quadratic discriminant analysis ( QDA ). Arg, Tyr and Ala, showed the highest correlations with the foliar damage in the PLS model and they could be responsible to improve cold resistance to the studied genotypes.

Foliar Damage Assessment and Selection of Cold Resistant Genotypes Using near Infrared Spectra of Eucalyptus Globulus Leaves

Near infrared (NIR) spectroscopy was used to predict cold resistance in Eucalyptus globulus genotypes after acclimatation treatments at low temperatures. Branches of the genotypes were maintained during 31 days in three cold chambers and the NIR spectra of milled leaves were obtained. The samples were subsequently exposed to artificial freezing (with some branches exposed to −2°C) and the foliar damage was assessed by visually estimating the necrotic area of each leaf. These values were used as reference parameters to evaluate cold resistance in the genotypes. A partial least squares (PLS) method was performed using the foliar damage and the NIR spectra of leaves. Spectra were treated with multiplicative scatter correction (MSC) and orthogonal signal correction (OSC). An excellent model was achieved which predicted foliar damage in the genotypes with a low standard error of prediction (3.5%), a high regression coefficient in cross-validation and external validation ( r > 0.9) and a high percentage of the variance explained by the spectra (95.4%). Furthermore, a pattern recognition method, using a regularised discriminant analysis (RDA) of the scores matrix obtained in PLS, in a denominated PLS/RDA on scores strategy, was applied directly to the spectra to classify each genotype as tolerant or sensitive; 100% of the genotypes were correctly assigned. These results demonstrate the advantages of using the NIR spectra of leaves as a rapid, nondestructive tool to evaluate cold resistance in genotypes.

Les variations longitudinales intra-arbre des propriétés papetières et du bois varient entre les génotypes d’Eucalyptus globulus

Wood discs were sampled from 6 heights up the stem of 248 trees representing 10 subraces and 116 families grown in an E. globulus base-population progeny trial. The lower stem had the least favourable wood properties for kraft pulpwood and most solidwood applications: bark was thickest, basic density was lowest and kino, decay and shrinkage traits were greatest at or below 12% of tree height. Significant genetic differences at the subrace level were revealed in diameter, bark thickness, basic density, decay and gross shrinkage and at the family within subrace level in diameter, basic density and decay. However, subrace-by-height-category interactions in bark thickness, basic density, decay and gross shrinkage indicated that differences among subraces were dependent on height in these traits. Examination of longitudinal trends revealed some evidence that the zone of thick basal bark extended further up the stem in thicker-barked subraces and that the Southern Tasmania subrace might be less effective than other subraces in restricting the longitudinal spread of decay after infection.